1. Technical Field
The present invention relates to magnetoresistance effect elements and methods for manufacturing the same, and magnetic memory devices.
2. Related Art
In recent years, magnetic memory devices (MRAMs: Magnetic Random Access Memories) are attracting attention as memory devices that can be alternatives to DRAMs (Dynamic Random Access Memories) and SRAMs (Static Random Access Memories). MRAM are advantageous because they are nonvolatile, and capable of high-speed operations and higher recording density, and therefore are viewed as promising data storage memories and system memories for portable electronic equipment (see, for example, Wang et al., IEEE Trans Magn. 33 (1997), 4498).
A MRAM is equipped with tunneling magnetoresistance elements (TMR elements) each having a ferromagnetic tunneling junction structure formed from a ferromagnetic layer/insulating layer/ferromagnetic layer as a memory cell, and stores differences in the tunneling resistance in the insulating layer caused by changing of the spin direction (parallel/anti-parallel) of the ferromagnetic layers that sandwich the insulating layer in the TMR element, in association with data “1” and “0.”
In order to operate an MRAM stably, it is important that a stable tunneling effect can be obtained at each of the TMR elements, and the magnetic characteristic of each of the ferromagnetic layers and the uniformity of the insulation layer composing the element greatly affect the tunneling effect. For example, the insulation layer needs to be formed thin to about 1 nm, and variations in its film thickness need to be suppressed below 10%. Also, in order to obtain a good magnetic characteristic in the magnetic layers, it is important to form them with a uniform film quality. In particular, when they are composed of crystalline magnetic thin films, their magnetic characteristic is greatly influenced by the crystallinity.
However, the ferromagnetic layer is generally formed on an insulating film that is composed of an oxide having an amorphous structure such as silicon oxide, and it is difficult to form an epitaxial film on such an insulating layer. Accordingly, there is a problem in that it is difficult to obtain a ferromagnetic layer having a good crystallinity.
The present invention has been made in view of the problems of the conventional technology, and its object is to provide magnetoresistance effect elements equipped with magnetic layers having good crystallinity and excellent magnetic characteristic, and methods for manufacturing the same. It is also an object of the present invention to provide magnetic memory devices that excel in operation stability.